Some general tips that I've found helpful in building coasters in any coaster building game:
Always graduate your heights throughout the coaster - try and make the next element (whatever it is) about 85% of the height of the previous element
bank every single corner, and the faster you want the corner to be taken the more you want to bank - this makes corners smoother and keeps speed up. Also faster corners will normally need a longer, more gradual bank so they don't snap straight to a 60 degree banking
bank into and out of elements the same way to smooth out to a straight run, and try to create a straight section (however big or small) in between changing banking direction
try and make any inversions have a fairly slow top out moment - the slowest point of the inversion should be the upside down part. Play with the element size (bigger to slow it down, smaller to speed it up)
loops in general can be entered at a fairly high speed, but corkscrews, barrel rolls and inline twists should be fairly slow so try to use those towards the end of the ride unless you combine them with half loops (cobra rolls, Immelmanns and dive loops
Block brake sections are a good way to slow your coaster down and give you a half way point that can then set your speed accordingly for the next sections
General tips for coaster types:
looping/inverted coasters tend to do better when the track kind of interlinks with itself, so switchbacks, tracks through the loop element, corkscrew over corkscrew etc. Try and avoid long straight sections that take the ride away from a central point
Hyper/giga coasters with no loops usually focus on air time, big hills and long corners, so these tend to run the opposite of looping coasters.
kiddie coasters tend to have the smallest footprint and usually stick to helixes and turns within turns. The track is also much shorter, usually only lasting 15 - 20 seconds a lap
As has been suggested look at real world examples and try to incorporate layout and pacing from them. Also it may be worth practicing with some generic real world coaster layouts and play around with how you get to and from each element:
Looping coaster: Lift hill > bank turn left/right to downhill > loop > air time hill > Cobra roll > air time hill > Immelmann/dive loop > bank curve to brake block ? downhill to corkscrew > left/right helix > corkscrew/inline twist /barrel roll > brake run > station
The biggest problem normally in custom coasters is speed and banking. Play around with the heights throughout the coaster to get a good handle on how to manage speed, then start focusing on banking in main corners, then banking into/out of elements if needed. A lot of it is trial and error
The good thing with Planet Coaster is you can have the coaster run in test phase while you build so you have a visual indicator as you're making things. Also I imagine things might become clearer once ride analytics are impemented fully
